Climate change and Vulnerability Assessment: Water-borne disease

Transcription

1 Climate change and Vulnerability Assessment: Water-borne disease AVEC Summer School Peyresq September 2003 Mike Ahern Research Fellow London School of Hygiene and Tropical Medicine

2 AIM OF LECTURE Provide an overview of the methodological challenges in conducting vulnerability assessments for the health impacts of climate change

3 OUTLINE OF LECTURE 1. Climate change impacts on health 2. Vulnerability, and water-related disease 3. Global Burden of Disease diarrhoeal disease 4. Vulnerability Assessment some conclusions

4 Climate change impacts on health

5 WHAT IS PUBLIC HEALTH? Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. [WHO, 1946] focus on whole populations broad definition of health population health depends not only on the provision of good healthcare services but also on the physical, social, cultural and economic environment in which people live

6 Health determinants Bio-physical Social

7 PATHWAYS BY WHICH CLIMATE CHANGE MAY AFFECT HEALTH based on Patz et al REGIONAL WEATHER CHANGES: Moderating influences HEALTH EFFECTS Temperature-related illness, death Flood, storm-related health effects CLIMATE CHANGE - heatwaves - extreme weather - temperature - precipitation Air pollution levels Contamination pathways Transmission dynamics Air pollution effects Water- and food borne diseases Vector-borne and rodent-borne disease Adaptation measures

8 Complex interactions between, water, climate and health Source: Adapted from Ahern, M.J. and McMichael, A.J. (2002) Climate change Land degradation Diverse pathways Agroecosystem productivity Altered precipitation Human Health Conflict Declines in phenotypic, genetic materials and diverse goods and services Water quality (safety) and quantity Biodiversity loss and ecosystem function Freshwater decline

9 Typology of water-related related transmission route for infections infections (Cairncross and Feachem, 1993) Transmission route Water-borne: humans become infected by drinking water containing infectious pathogen Water-washed (or water-scarce): infection influenced by quantity of water available Water-based: disease where pathogen spends part of its life-cycle in a water snail or other aquatic animal Water-related insect vector: pathogen spread via insects which breed in water or bite near water Examples of disease Cholera, Typhoid Scabies, Trachoma Schistosomiasis Malaria, Yellow fever, Dengue

10 Water-borne disease 1 Complex relationships between human health and problems of water quality, availability, sanitation, and hygiene Predicting potential impacts of climate change difficult because access to a clean safe water supply determined primarily by socioeconomic factors Water scarcity may necessitate use of poorer quality sources of freshwater, such as rivers, which often are contaminated

11 Water-borne disease 2 Excessive precipitation can transport terrestrial microbiological agents into drinking-water sources Outbreaks of cryptosporidiosis, giardia, and other infections triggered by heavy rainfall events in UK and United States (Lisle and Rose, 1995; Atherholt et al., 1998; Rose et al., 2000; Curriero et al., 2001) Significant correlation between cumulative monthly distribution of cholera cases and monthly distribution of precipitation observed in Guam (Borroto and Haddock, 1998)

12 Water-borne disease 3 Water-borne (and food-borne) diseases tend to show marked seasonality, peaks in early spring or summer Higher temperatures favour micro-organism proliferation and often are associated with an increase in gastrointestinal infections Above-average temperatures in Peru during the El Niño associated with a doubling in the number of children admitted to hospital with diarrhoea (Checkley et al., 2000)

13 Admissions for diarrhoea, mean ambient temperature, and relative humidity in Lima, Peru, 1 Jan 1993 to 15 Nov Source: Checkley W, et al. Lancet 2000; 355: 44250

14 Vulnerability

15 Vulnerability 1 Vulnerability degree to which individuals and systems are susceptible to or unable to cope with the adverse effects of climate change And is a function of: The Exposure to the weather or climate-related hazard Sensitivity extent to which health, or the natural or social systems on which health outcomes depend, are sensitive to changes in weather and climate (the exposure-response relationship) Adaptive capacity measures and actions in place to reduce the burden of a particular adverse health outcome. The effectiveness of these interventions partially determines the exposure-response relationship (WHO, 2003)

16 Vulnerability 2 Individual factors disease status (people with pre-existing poor health may be more vulnerable to direct effects); Socioeconomic factors (in general, the poor are more vulnerable; Demographic factors (infants are more vulnerable to diarrhoeal diseases) Community factors- integrity of water and sanitation systems and their capacity to resist extreme events; access to information, including early warnings of extreme climate events Geographical factors influence of f El Niño cycle or occurrence of extreme weather events; low-lying coastal populations more vulnerable to effects of sealevel rise

17 Global Burden of Disease

18 Global Burden of Disease (GBD) 1 What will be the total health impact caused by climate change, for the years 2000, 2001, 2005, 2010, 2020, 2030? How much of this impact could be avoided by reducing the risk factor (i.e. stabilizing greenhouse gas emissions)?

19 OVERVIEW OF GBD PROCESS FOR CLIMATE CHANGE Greenhouse gas emissions scenarios Defined by IPCC Time Global climate modelling: Generates series of maps of predicted future distribution of climate variables 2080s 2050s 2020s Health impact model Generates comparative estimates of the regional impact of each climate scenario on specific health outcomes Conversion to GBD endpoints (DALYs) e.g. based on regression analysis 2020s 2050s 2080s Level Age group (years)

20 GBD Outcome Class Direct impacts of heat and cold Food and water-borne disease Vector-borne disease Natural disasters Risk of malnutrition Outcome Incidence of cardiovascular disease deaths Incidence of diarrhoea episodes Incidence of malaria and dengue cases Incidence of deaths due to unintentional injuries Incidence of other unintentional injuries (non-fatal) Prevalence of non-availability of recommended daily calorie intake

21 HEALTH IMPACT EXAMPLE: INCIDENCE OF DIARRHOEA CASES

22 Causal web for climate change effects on diarrhoeal disease (relative importance of pathways varies between pathogens). Source: McMichael, A.J. et al (2002) Distal causes Proximal causes Infection hazards Outcome Temperature, Humidity, Precipitation Survival/ replication of pathogens in environment Consumption of contaminated water Living conditions (sanitation and water supply) Food sources and hygiene practices Contamination of water resources Contamination of food sources Rate of personperson contact Consumption of contaminated food Contact with infected persons Vulnerability (e.g. age, nutrition) Incidence of mortality and morbidity attributable to diarrhoea

23 HOW MUCH WILL DIARRHOEA INCREASE WITH CLIMATE CHANGE? 1) Overlay maps of projected temperature change on country maps, using a Geographic Information System 2) For each country with GDPpc < US $6000, multiply temperature increase by 1.05 (=5% increase per C 0 increase in temperature) 3) Calculate average increase in incidence for each WHO region

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25 PREDICTED MEAN TEMPERATURE CHANGE BAU S750 S550

26 ESTIMATED DEATH RATE FROM DIARRHOEA (2000) Total Deaths Death rate/1000 pop. Afr D Afr E Amr A Amr B Amr D Emr B Emr D Eur A Eur B Eur C Sear B Sear D Wpr A Wpr B WHO World Health Report 2001

27 Relative Risk Afr D Afr E Amr A Amr B Amr D Emr B Emr D Eur A Eur B Eur C Sear B Sear D Relative Risk of Diarrheoa in 2030, by Region Wpr A Wpr B Climate scenarios, s550 as function s750 of GHG emissions UE

28 GBD Diarrhoeal diseases Relative risk for 2030 in developing regions estimated to be under unmitigated emissions compared to baseline climate Richer countries (GDP > $6000/year) will suffer little Uncertainties due to poor characterisation of variations in relationship between climate and diarrhoea in more or less developed regions, which have different balances between pathogens preferring higher or lower temperatures

29 GBD Considerable uncertainties around these estimates. Climate change obscured by natural climate variability, and effects health through complex causal pathways Coupled with poor health surveillance in most vulnerable populations = inherently difficult to directly measure health losses or gains attributable to climate change Uncertainties could be reduced by 1. Applying projections from several climate models 2. Relating climate and disease data from a wider range of climatic and socioeconomic environments 3. More careful validation against patterns in the present or recent past

30 GBD Long-term climate change effects are slow and difficult to measure with confidence Lack of good long term data series >20 years Analyses are affected by the confounding effects of long-term changes in other [non-climate] causative factors Although, it simpler and quicker to measure the health effects of climatic variation either over short time periods (seasonal or inter-annual), or with geography, the attribution to climate change is indirect...

31 Europe Water-borne disease Impacts in European Region not as great as other regions, e.g. Sub-Saharan Africa, South Asia Some populations in eastern Europe with restricted access to water in the home would be vulnerable to any climate related decreases in freshwater availability The most significant water-borne disease associated with the public water supply in western Europe is cryptosporidiosis Increases in the frequency or intensity of extreme precipitation events can increase the risk of outbreaks of this disease

32 Evidence of Health Impacts of Climate Change Little evidence that recent trends in regional climates have affected health outcomes in human populations Could reflect a lack of such effects to date or difficulty in detecting them against a noisy background containing other more potent influences on health Causation of most human health disorders is multi-factorial and the socioeconomic, demographic, and environmental context varies constantly Infectious diseases no single epidemiological study has clearly related recent climate trends to a particular disease Various studies of the correlation between interannual fluctuations in climatic conditions and occurrence of malaria, dengue, cholera, and other infectious diseases have been reported

33 Vulnerability Assessment 1 One way of integrating various stresses on populations and regions arising from climate change (IPCC, 2001) Methods and tools for evaluating vulnerability are in formative stages of development Further development of methods and tools for vulnerability assessment warranted, especially for the human dimensions of vulnerability, integration of biophysical and socioeconomic impacts, and comparison of regional vulnerability.

34 Vulnerability Assessment 2 Uncertainties regarding the sensitivity of many health outcomes to climate or climate-induced environmental changes Little quantitative research, with estimation of exposure-response relationships, for outcomes other than death rates associated with thermal stress and changes in the transmission potential of several vector-borne infectious diseases Increased effort to map current distribution of vectors and diseases, e.g. malaria using climate and other environmental data (including satellite data).

35 Vulnerability Assessment 2 Not yet clear what criteria are most appropriate for assessment of climatic influences on changes in infectious disease patterns Inherent difficulty in detecting small climate-induced shifts in population health outcomes and in attributing the shift to a change in climate

36 Vulnerability Assessment 4 Formal methods of choosing indicators and combining them into meaningful composite indices must be tested Combining qualitative insight and quantitative information is difficult but essential to full assessments Finally, improved methods and tools should facilitate comparison of vulnerability profiles between at-risk regions and populations and highlight potential reductions in vulnerability, through policy measures or the beneficial effects of climate change

37 Acknowledgements Diarmid Campbell-Lendrum, WHO Paul Wilkinson and Sari Kovats, LSHTM

38 THANK YOU